In recent years as an environmentally friendly vehicle, electric powered vehicles such as an electric vehicle, hybrid vehicle and fuel cell vehicle have been developed into practical use. An electric powered vehicle has mounted thereon an electric motor generating force to drive the vehicle, and a power supply system including a power storage device for supplying electric power to drive the motor.
Particularly, there has been proposed a configuration for charging a vehicle-mounted power storage device in a hybrid vehicle by means of a power supply external to the vehicle (hereinafter also referred to as an “external power supply”), and accordingly, there is a demand for increasing the travel distance allowed through the electric power stored in the vehicle-mounted power storage device. Hereinafter, charging a vehicle-mounted power storage device by an external power supply will also simply be referred to as “external charging”.
For example, Japanese Patent Laying-Open No. 2008-109840 (Patent Document 1) and Japanese Patent Laying-Open No. 2003-209969 (Patent Document 2) describe a power supply system having a plurality of power storage devices (batteries) connected in parallel. The power supply system described in Patent Document 1 and Patent Document 2 is provided with a voltage converter (a converter) for each power storage device (battery) as a charging/discharging adjustment mechanism. In contrast, Japanese Patent Laying-Open No. 2008-167620 (Patent Document 3) describes a power supply device in a vehicle having a main power storage device and a plurality of sub power storage devices mounted thereon, including a converter corresponding to the main power storage device and a converter shared by the plurality of sub power storage devices. This configuration is advantageous in that the storable amount of energy is increased while the number of elements constituting the device can be suppressed.
In particular, the configuration described in Patent Document 3 has one of the plurality of sub power storage devices selectively connected to the converter to allow the main power storage device and the selected sub power storage device to supply driving power for an electric motor to drive the vehicle. When the sub power storage device in use has a decreased state of charge (SOC) in the power supply device, a different sub power storage device is newly connected to the converter such that the plurality of sub power storage devices are sequentially used to increase the travel distance allowed through the stored electric energy (EV (electric vehicle) travel distance).